A satellite flying in Earth orbit is subjected to a particle (electron and proton) radiation environment, the severity being dependent on the orbit. This exposure to radiation has always been an issue for satellites. Standard integrated circuits can gradually degrade or even catastrophically fail when exposed to the space radiation environment thereby necessitating special radiation-hardened components for satellites. Radiation remains one of the leading causes of satellite anomalies; and as technology advances, the risk increases.
Throughout the years, the radiation effects community has developed models and devices to measure the effects of radiation on spacecraft components. Most commonly, the effects encountered in space radiation environments on materials and components are quantified using ground-based radiation testing. Depending on particle type and energy, the effects from space radiation interacting with a spacecraft or its systems can be classified into three main groups:
1. Single Event Effects (SEE): Single interactions, either large ionization or a nuclear reaction, that can give temporary or permanent damage to a given detector or system. SEE effects are important for digital circuits such as memories or microprocessor by inducing errors, undesired latch-ups and may lead to system failure.
2. Total Ionization Dose (TID): Effects caused by long-term exposure to ionizing radiation. TID may induce changes in the mechanical and electrical properties of materials, causing them to operate incorrectly or even fail. TID effects are important for insulators, cabling, CMOS circuits (due to charge build-up), optical elements and cryogenics.
3. Displacement Damage (commonly called Non-Ionizing Energy Loss (NIEL) damage): Displacement damage caused by long-term exposure to particle radiation such as neutrons, protons, heavy ions, and electrons. Some energetic particles can originate displacement defects in semiconductor materials, such as silicon sensors and solar cells, leading to introduction of deep band-gap levels with corresponding increase of noise and decrease of efficiency. Displacement damage effects are important for semiconductor devices, such as optical sensors, laser diodes, optocouplers, bipolar transistors, and solar cells.
Spacecraft charging is also a very important effect but is often mitigated through proper spacecraft design. Each of these main groups has established specific ground-based radiation testing methods to fully quantify the radiation survivability of materials and microelectronic devices; however, the options for quantifying displacement damage effects are limited.
Ionizing dose can be calculated by combining the particle fluence with the ionizing stopping power (or linear energy threshold, LET) of a given material. In an analogous manner, the displacement damage dose (DDD, in units of MeV/g) can be determined by combining the particle fluence and the nonionizing energy loss (NIEL), which is the rate at which atomic displacements are produced in a material from recoiling atoms caused by primary radiation particles such as electrons and protons. The NIEL calculation typically involves knowledge of the differential scattering cross for atomic displacements, the recoiling atom kinematics, and a term called the Lindhard partition factor, which separates out the nonionizing and ionizing energy loss components of the recoiling atom. There are primarily two physical interactions contributing to the total NIEL: 1) screened Coulombic and 2) nuclear. The nuclear component only becomes important for positive atoms having energies >10 MeV/AMU.
Displacement damage dose has been shown to be very effective in correlating the effects of differing energetic particles on the performance of several devices. As an example, consider electron and proton radiation effects on solar cells. To fully qualify a solar cell for space application, the heritage model developed by the California Institute of Technology/Jet Propulsion Laboratory (JPL) requires ground irradiation testing to be performed at several electron and proton energies. The testing provides ground based irradiation results performed on single junction GaAs solar cells where the degradation of the maximum power (Pmax) under 1 sun, AMO (25° C.) illumination conditions can be plotted as a function of particle fluence (# particles/cm2) for several electron and proton energies. In the JPL model, these data can be used to generate a set of relative damage coefficients (RDCs) from which the degradation performance can be predicted behind different shielding levels from both proton and electron energy spectra. This method can be used to properly size and/or shield (with coverglass) the solar array to meet mission end-of-life (EOL) requirements. This “heritage” approach is rigorously correct but requires a significant amount of ground-based irradiation data and can be very costly and time consuming.
Accordingly, a need remains in the art for a microelectronic device that can be used to accurately and simply quantify displacement damage dose directly.